This invention relates to pet foods and, more particularly, to an improved process for preparing meat-containing pet foods of the shelf-stable, intermediate-moisture variety.
Prior to the 1960's, animal foods were sold either in dry or canned form. The dry variety of animal foods usually contained less than 10% moisture and, hence, did not require sterilization procedures or refrigeration in order to render them resistant to microbial decomposition. The dry animal foods, however, were generally characterized by their low degree of palatability, it being found that as a general rule, palatability was enhanced at higher moisture contents.
Canned animal foods have offered a significant degree of palatability owing primarily to their high moisture contents, typically in the area of 75%. However, these high moisture contents required sterilization, generally by retorting, and refrigeration once the canned product was opened. Thus, canned foods had the disadvantages of high processing costs and reduced consumer convenience.
A significant contribution to the pet food field was made by Burgess et al in U.S. Pat. No. 3,202,514. Therein is described an intermediate-moisture animal food based principally upon proteinaceous meaty materials, which is shelfstable and resistant to microbial decomposition without the need for sterilization, refrigeration or aseptic packaging. Foods of this type contain, typically, 15 to 30% water and are stabilized against deterioration by "water soluble solutes", principally sugar. The function of these solutes is to bind the water present and make it unavailable for supporting microbial growth.
While the product of Burgess et al advanced the state of the art, the process for preparing it still required the use of freezing or refrigeration to store the meats prior to processing in the formulation. The freezing and refrigeration of meats both require large capital investments and entail large continuing costs for energy and labor. In the case of frozen meats, the meats are usually shipped in blocks which must be stored in suitable warehouses prior to use. The blocks are then hand loaded onto conveyers which feed them into choppers wherein they are chopped prior to being fed to the cooking and blending operations. Refrigerated storage is likewise costly.
Thus, the meat has been handled by costly conventional procedures since the time of Burgess et al despite the fact that the technology taught by that patent enabled the marketing of meat in unconventional form.
More recent patents have extended the technology of shelf-stable, meat-containing food products to include those which are higher in moisture and contain lower sugar levels. Exemplary of these is U.S. Pat. No. 3,985,904 to J. W. Bernotavicz wherein a cooked, proteinaceous meaty material, having a moisture content of above 50% by weight and a water activity above 0.90, is maintained in a shelf-stable condition by virtue of sufficient non-toxic acids and an effective amount of antimicrobials.
In another variation of the shelf-stable meat concept, U.S. Pat. No. 4,001,445 to Horrocks et al describes a process which retains the substantially raw appearance and characteristics of meat chunks by infusion with sufficient edible water soluble solute to stabilize it against microbial spoilage and then packing the infused material in the absence of oxygen. This reference, discloses that chunks of raw meat can be stabilized without the need to grind the meat into fine particles as is discussed in the Burgess et al and Bernotavicz patents cited above which are representative of the method of processing meat in this regard.
Horrocks et al teaches infusing chunks of meat with sufficient water binder to obtain an A.sub.w of less than 0.85. With this low A.sub.w, the product, like that of Burgess et al, will remain stable indefinitely. Stability of this duration would, according to the patent, allow shipment where refrigeration was not available. The moisture contents of these chunks is around 30%, typical for intermediate-moisture meats.
The introduction of large pieces of raw meat and meat by-products directly into the process stream according to current technology presents problems of process control. These meats exhibit wide variations in moisture, protein and fat contents, which are detrimental to the efficient production of intermediate-moisture pet foods. Acceptable commercial products must be shelf-stable and meet nutritional guarantees, as well as be highly palatable and provide good value to the purchaser. Where variabilities in essential product and process parameters are not properly noted and adjusted for prior to mixing the meat components with the remainder of the pet food ingredients, correction is usually possible only by the addition of more costly materials to make up for the deficiencies in the blend. Moreover, because present technology results in highly variable meat slurries which can cause these extra costs as well as the need to re-work more material should final product not meet quality control standards, quality control testing must be more frequent than would be desired.